1. Field of the Invention
The present invention relates generally to a composition for preventing tooth decay, and more particularly to a tooth-decay preventing composition containing hydroxy-apatite and a fluoride, wherein at least either one or the hydroxy-apatite or fluoride is microencapsulated or coated, and moreover a tooth-decay preventing composition, wherein compositions containing hydroxy-apatite and a fluoride coexist in an unmixed state.
2. Description of the Prior Art
Fluorides are known to be effective in preventing tooth decay by virtue of such effects as strengthening of the enamel, suppression of the enzymatic action of bacteria which convert saccharides into acids, and suppression of the propagation of microorganisms relating to the corrosion destruction of enamel and dentine. Sodium fluoride, sodium monofluorophosphate, stannous fluoride and the like (hereinafter referred to simply as fluorides) are used for dentifrice compositions. However, to use a fluoride for dentifrice compositions in an amount sufficient to be really effective in preventing tooth decay is deemed by same as being impossible, since the amount of fluorine that can be incorporated in dentifrice compositions as fluoride is limited to 1,000 ppm or less, because of the toxicity of fluorine itself. Thus, the development of compositions sufficient to produce a decay preventive effect using an amount of fluorine within the set limits is still being awaited. On the other hand, hydroxy-apatite serves to absorb dental plaque responsible for tooth decay, while simultaneously it adheres to the surfaces of teeth, and thereby promoting the recalcification and strengthening of teeth. For this reason, hydroxy-apatite is added to dentifrice compositions as a satisfactory decay preventive. Accordingly, if a composition could be prepared containing hydroxy-apatite and a fluoride in such a way that they might exhibit a synergistic effect, then it would be expected that an ideal tooth-decay preventing composition could be obtained. However, it has been found that mixing of hydroxy-apatite with the fluoride causes easy conversion of hydroxy-apatite into apatite fluoride and calcium fluoride. Apatite fluoride and calcium fluoride fail to exhibit the decay-preventing action that the fluoride has, since they serve neither to absorb dental plaque nor recalcify and strengthen teeth. Besides, they are not absorbed onto the surfaces of teeth. Thus, although hydroxy-apatite and the fluoride are independently effective for the prevention of tooth decay, no tooth-decay preventing effect whatsoever is obtained with a composition wherein they exist together freely. For these reasons, a tooth-decaying preventing composition containing both the fluoride and hydroxy-apatite is not available in the prior art.